Networks that primarily utilize data link layer devices are often referred to as layer two (L2) networks. A data link layer device is a device that operates within the second layer of the Open Systems Interconnection (OSI) reference model, i.e., the data link layer. One example of a common L2 network is an Ethernet network in which end point devices (e.g., servers, printers, computers) are connected by one or more Ethernet switches. The Ethernet switches forward Ethernet frames, also referred to as L2 communications or L2 packets, to devices within the network. As the Ethernet switches forward the Ethernet frames the Ethernet switches learn L2 state information for the L2 network, including media access control (MAC) addressing information for the devices within the network and the physical ports through which the devices are reachable. The Ethernet switches typically store the MAC addressing information in MAC tables associated with each of their physical interfaces. When forwarding an individual Ethernet frame, an ingress port of an Ethernet switch typically broadcasts the Ethernet frame to all of the other physical ports of the switch unless the Ethernet switch has learned the specific physical port through which to the destination MAC address devices is reachable. In this case, the Ethernet switch forwards a single copy of the Ethernet frame out the associated physical port.
One type of large area L2 network connectivity being developed is referred to as “Metro Ethernet” in which Ethernet is used as a metropolitan access network to connect subscribers and businesses to a larger service network or the Internet. Various types of Ethernet services have been defined to provide different forms of connectivity. One type of metro Ethernet service, referred to as “E-TREE” service, has recently been defined in which Ethernet communication is constrained to point-to-multipoint (P2MP). With E-TREE service, each endpoint L2 device is designated as either a root or a leaf. L2 devices designated as roots are permitted to communicate with all other endpoints on the E-Tree. However, L2 devices designated as leafs on the E-tree are permitted to communicate only with L2 devices that are designated as root devices.
The Internet Engineering Task Force (IETF) has proposed Metro Ethernet E-Tree support in multi-protocol label switching (MPLS) networks, including those utilizing the Virtual Private LAN Service (VPLS), also known as Transparent LAN Service and Virtual Private Switched Network service. The VPLS service offers a Layer 2 Virtual Private Network (VPN) in which the customers in the VPN are connected by a multipoint Ethernet LAN. One example proposal for providing E-TREE service over VPLS can be found in “Requirements for MEF E-Tree Support in VPLS,” draft-key-12vpn-vpls-etree-reqt-02.txt, Oct. 7, 2010, hereby incorporated by reference in its entirety. Further details of VPLS can be found in, Kompella & Rekhter, Virtual Private LAN Service (VPLS), “Using BGP for Auto-Discovery and Signaling,” IETF, January 2007, hereby incorporated by reference in its entirety.
However, certain difficulties may arise when deploying conventional E-TREE service, especially in VPLS environments. For example, problems may arise when root and leaf nodes are connected to the same router or other network device that provides access to the VPLS core. In such cases, other routers providing the E-TREE service over the VPLS core often cannot distinguish any root traffic and leaf traffic sourced by the router, which makes it difficult to comply with the forwarding constraints of the E-TREE service. As a result, some vendors have simply required that their customers avoid such deployments.
Furthermore, service provides may utilize different types of access networks for providing connectivity to customer networks for which the E-TREE service may be deployed. In some cases, connectivity to the VPLS core may be provided to the customer networks by the service provider using point-to-point spoke VLANs through an intermediate access network. In other cases, L2 network connectivity may take the form of provider bridging in accordance with IEEE standards 802.1ad and 802.1q. Provider bridging defines an architecture in which a service provider provides one or more service VLANs (“S-VLANS) to service and isolate L2 traffic from customer networks. This allows customers to effective run their own VLANs inside the VLAN provided by the service provider. Further details of provider bridging can be found in Institute of Electrical and Electronics Engineers, Inc., IEEE P802.1ad, “Provider Bridges,” May 26, 2006, hereby incorporated by reference in its entirety.